1. Field of the Invention
This invention relates to an oil pan for an internal combustion engine, and more particularly to improvements in an oil pan structure with which the lubrication oil is positively returned into sump.
2. Description of the Prior Art
It is well known that an internal combustion engine is provided with an oil pan as shown in FIG. 3. In FIG. 3, a multiple cylinder internal combustion engine 1' comprises a cylinder block 2' which rotatably supports a crankshaft 3'. An oil pan 4' is connected to the under surface of the cylinder block 2'. The oil pan 4' includes a sump section 5' and a shallow bottom section 6' which are disposed along the axis of the crankshaft 3' and under the crankshaft 3'. A baffle plate 7' having a cutout 8' is installed in the sump section 5'. An oil sucking section 9' which has an oil strainer 10' at its end is inserted into the sump section 5' and dipped in lubrication oil through the cutout 8', so that the oil sucking section 9' can suck the lubrication oil.
In recent years, there has been a tendency that a vehicular engines are smaller and more light-weight. Accordingly, the oil pan 4' has become shortened in height. Additionally, counterweights 11' installed in the crankshaft 3' have become located slightly above the oil pan 4'. Therefore, when the oil level 13' of the lubrication oil in the oil pan 4' is changed into an inclined condition under inertial force caused by an outer force such as acceleration, deceleration, turning of the vehicle, he lubrication oil flows into the shallow bottom section 5'. The lubrication oil is then splahsed by blown air pressure caused by the rotation of the counterweights 11'. Under this condition, in case the oil level 13' is further, inclined in the direction to cause the lubrication oil to flow into the shallow bottom section 6', the counter weight 11', which is not dipped in the oil under the normal conditions, becomes dipped in the lubrication oil as shown in FIGS. 3 and 4. This causes the counterweight 11' to splash the oil. Therefore, the amount of the oil returned into the sump 5' is reduced, and therefore the oil level 13' is lowered. This causes a problem that an oil pump (not shown) cannot supply the oil to lubricate the required sections. In contrast, it has been proposed that the guide plate 23' returning the splashed oil toward the oil level is installed at a side surface 22' of an oil pan 21' as shown in FIGS. 5 and 6. Such an arrangement is disclosed, for example, in U.S. Pat. No. 4,270,497. However, since the guide plate 23' only downwardly guides the splashed oil and does not guide the oil from a shallow bottom section 24' toward a sump 25', a lack of the lubrication oil in the sump 25' is possibly caused under the influence of the oil viscosity or like.